The c-Myc oncogenic transcription factor plays a key role in many human cancers through the regulation of gene expression. Although how Myc regulates gene expression is better defined, the groups of genes that Myc regulate are just emerging from a variety of different experimental approaches. Studies of individual Myc target genes and their functional implications are now complemented by large datasets of Myc target genes through the use of subtraction cloning, DMA microarray analysis, SAGE, ChIP, and genome marking methods. We have annotated these data in a Myc Target Gene database (www.myccancergene.org). Myc target genes appear to respond to Myc in a context dependent manner. In particular, how other transcription factors collaborate with Myc to regulate these genes as well as cell type specific effects need further study. To fully appreciate the differences between physiological Myc function and deregulated Myc function in tumors, the challenge is to delineate how the Myc-responsive transcriptomes influence the various phenotypes induced by Myc. Specifically, we hypothesize that under physiological conditions, Myc cooperates with specific transcription factors to promote gene expression, while under pathological, high Myc expression, Myc is able to induced a distinct set of ectopic Myc target genes that contribute to tumorigenesis. To reach our long-term goal of understanding Myc in human cancers we set the following Specific Aims: Aim 1. To determine differences between the physiological and pathological Myc target gene networks and identify downstream target hubs that encode transcription factors and other key signal transduction proteins. Aim 2. To maintain and improve the Myc target gene database. Aim 3. To identify transcription factors that cooperate with Myc in regulating downstream targets. Aim 4. To determine the molecular mechanisms by which Myc collaborates with the hypoxia inducible transcription factor, HIF1, in regulating hypoxia-responsive genes vital for tumor survival such as those encoding glycolytic enzymes.